i86 ZYGNEMATACEAE 



PLATE XXI 



Spirogyra 



Fig. I. — 5. communis, gametangia and zygospores from Illinois. Fig. i. 

 — 5. intorta, conjugating filaments and zygospores from Szechwan, China. 

 After Jao. Fic. 3. — S. juergensii, typical gametangia and zygospores from 

 Illinois. Fig. 4. — S. singularis, gametangia and zygospores from Illinois. 

 Fig. 5.- — S. gracilis, gametangia and zygospores from Ohio. Fig. 6. — S. 

 jragilis. gametangia and zygospores. Note separation of receptive gam- 

 etangia following conjugation, from Szechwan. After Jao. Fig. 7. — S. sil- 

 i'icola, gametangia and zygospores from northern Illinois. After Britton. 

 Fig. 8. — S. teodorcsci, gametangia and zygospores from Illinois. Figs. 9- 

 10. — S. vartjormis, vegetative cell, gametangia, and zygospores variously 

 deformed by the gametangial walls from Cape Town, South Africa. 

 Fig. II. — S. condensata, lateral and scalariform conjugation, vegetative cell, 

 and zygospores from Charleston, Illinois. Figs. 12-14. — 5. pseudovarians, 

 gametangia, zygospores, and optical section of spore wall from Czecho- 

 slovakia. After Czurda. 



